Transthyretin (TTR) is a secreted thyroid hormone-binding protein. TTR binds and transports retinol binding protein (RBP)/Vitamin A, and serum thyroxine (T4) in plasma and cerebrospinal fluid.
Both normal-sequence TTR and variant-sequence TTR cause amyloidosis. Normal-sequence TTR causes cardiac amyloidosis in people who are elderly and is termed senile systemic amyloidosis (SSA) (also called senile cardiac amyloidosis (SCA)). SSA often is accompanied by microscopic deposits in many other organs. TTR mutations accelerate the process of TTR amyloid formation and are the most important risk factor for the development of clinically significant TTR amyloidosis (also called ATTR (amyloidosis-transthyretin type)). More than 85 amyloidogenic TTR variants are known to cause systemic familial amyloidosis. The liver is the major site of TTR expression. Other significant sites of expression include the choroid plexus, retina and pancreas.
TTR amyloidosis manifests in various forms. When the peripheral nervous system is affected more prominently, the disease is termed familial amyloidotic polyneuropathy (FAP). When the heart is primarily involved but the nervous system is not, the disease is called familial amyloidotic cardiomyopathy (FAC). A third major type of TTR amyloidosis is called leptomeningeal/CNS (Central Nervous System) amyloidosis.
Double-stranded RNA molecules (dsRNA) have been shown to block gene expression in a highly conserved regulatory mechanism known as RNA interference (RNAi). WO 99/32619 (Fire et al.) disclosed the use of a dsRNA of at least 25 nucleotides in length to inhibit the expression of genes in C. elegans. dsRNA has also been shown to degrade target RNA in other organisms, including plants (see, e.g., WO 99/53050, Waterhouse et al.; and WO 99/61631, Heifetz et al.), Drosophila (see, e.g., Yang, D., et al., Curr. Biol. (2000) 10:1191-1200), and mammals (see WO 00/44895, Limmer; and DE 101 00 586.5, Kreutzer et al.).
U.S. Publication No. 20070207974 (U.S. patent application Ser. No. 11/095,383, filed Mar. 30, 2005) discloses functional and hyperfunctional siRNAs. U.S. Publication No. 20090082300 (U.S. patent application Ser. No. 12/273,731, filed Nov. 19, 2008) discloses antisense molecules targeting transthyretin (TTR). U.S. Pat. No. 7,250,496 (U.S. patent application Ser. No. 10/310,914, filed Dec. 6, 2002) discloses microRNAs targeting transthyretin (TTR). WO 2010/048228 (International application no. PCT/US2009/061381, filed Oct. 20, 2009) and U.S. publication no. 20100120893 (U.S. patent application Ser. No. 12/582,669, filed Oct. 20, 2009) disclose compositions (e.g., siRNA) and methods for inhibiting expression of transthyretin (TTR).